The present invention relates to a flame insulative heat vulcanizable silicone rubber composition and flame insulative two-part room temperature vulcanizable silicone rubber composition and more particularly the present invention relates to such compositions having in them as the flame insulative additive from 25 to 150 parts of ground glass and more preferably, glass frits.
Heat vulcanizable silicone rubber compositions are well known. Such compositions usually consist of a linear diorganopolysiloxane polymer of 1,000,000 to 200,000,000 cps. viscosity at 25.degree. C., an inert filler which is usually selected from the reinforcing fillers such as, fumed silica and precipitated silica and also may contain to some extent extending fillers such as, quartz or zinc oxide. To such a mixture there is normally added a peroxide curing catalyst which cures the composition at elevated temperatures to form a silicone elastomer. In the past such heat vulcanizable silicone rubber compositions were utilized to insulate wires and cables of various kinds so as to protect or maintain the electrical integrity of the conducting wires or cables during a fire, that is, such heat vulcanizable silicone rubber compositions were found to be highly desirable as insulators for electrical wires and cables. Such silicone materials tended to resist burning better than organic materials and organic polymers. Such heat vulcanizable silicone rubber compositions even when burning leave a white ash which if kept in place would protect to a certain extent the underlying wires or cables from further burning and would tend to prolong the maintaining of the electrical integrity of the conducting wire or cable. In addition, there have been various modifications in which such heat vulcanizable silicone rubber compositions were made even more resistant to burning by the addition of small amounts of platinum alone or with carbon black as, for instance, disclosed in the Noble/Brower, U.S. Pat. No. 3,514,424. One difficulty with such flame insulative heat vulcanizable silicone rubber compositions was that the silicone elastomer that was formed would still, upon burning at highly elevated temperatures, form a white ash that was easily displaced from its place by gaseous by-products that were formed during the combustion process, and by physical vibration of the burned cable. Accordingly, it was felt highly desirable to develop a flame insulative heat vulcanizable silicone rubber composition which, upon burning, would form a white ash that maintained its physical integrity around the cable so as to form a barrier between the flame and the wire that was being protected so as to provide further flame protection capabilities to the wire that was enclosed by such heat vulcanizable silicone rubber composition. Other attempts have been made to keep the white ash that is formed when the silicone elastomer was burned in place such as, use of glass braids around the silicone elastomer. However, with the use of such glass braids, the resultant cable was bulky and hard to work with in the construction and installation of electrical systems.
The approach for the protection of such electrical conducting wires or cables when there was utilized a two-part room temperature vulcanizable silicone rubber composition as a sealant that was cured in place upon mixing the two parts and forcing the material in the cavities in the cable and allowing the composition to cure to a silicone elastomer, was such that the silicone material was kept in place during the burning process by the configuration and shapes that it took as it filled the voids of the electrical cables. The use of such a room temperature vulcanizable silicone rubber composition and in such a use is known to the industry as a valley sealant. It was common when such room temperature vulcanizable silicone rubber compositions were utilized as valley sealants that jackets were inserted thereover, as an additional means for keeping the white ash that was formed from the burning silicone elastomer in place. However, as stated previously, the jackets burned even more rapidly than the silicone elastomer and, thus, were not very effective, such that the valley sealant, upon burning, formed a white ash and such white ash still tended to be moved in its position by the gases that escaped and that were formed by the burning of the silicone elastomer. Accordingly, it was highly desirable for such two-part room temperature vulcanizable silicone rubber compositions that were used as valley sealants to have added to them additives that would maintain their integrity and result in the white ash that was formed from the burning of the silicone elastomer being cohesive so that the white ash of the burned silicone elastomer would remain in place and act as a barrier between the flame and the electrical conducting wires that were being protected by such room temperature vulcanizable silicone rubber composition. It should also be noted that the use of platinum as well as carbon black and various other additives to two-part room temperature vulcanizable silicone rubber compositions, while increasing to some extent the flame insulativeness did not perform any function as far as allowing the cured silicone elastomer that was burned into a white ash to maintain its integrity.
Accordingly, it is one object of the present invention to provide for an improved heat vulcanizable silicone rubber composition which has improved flame insulative properties by utilizing in the composition the necessary amount of ground glass and more specifically glass frits so that the silicone composition after it has burned to a white ash will still maintain its integrity.
It is another object of the present invention to provide for a process for producing the heat vulcanizable silicone rubber composition with improved flame insulative properties by the utilizing in such process ground glass or glass frits such that the composition after burning to a white ash still maintains its integrity.
It is an additional object of the present invention to provide for a two-part room temperature vulcanizable silicone rubber composition with improved flame insulative properties which by the use of ground glass or glass frits in the composition results in the composition maintaining its integrity upon burning.
It is yet an additional object of this invention to provide for an improved process for producing a two-part room temperature vulcanizable silicone rubber composition with improved flame insulative properties which by the addition of ground glass or glass frits in the composition results in the composition maintaining its integrity.
These and other objects of the present invention are accomplished by means of the disclosure set forth herein below.